All the valleys and gills of Swaledale contain sediments deposited by rivers and streams. These ‘alluvial’ deposits include silt, sand and gravel deposited between the end of the last glaciation and the present-day. Alluvial deposits form floodplains, river terraces (which represent former valley floor levels) and several small fan-shaped deposits where hill streams enter broad valleys. In many of the gills where lead mining had been active the former mining dumps and tailing heaps can provide additional sediment to the stream.
Floodplains lie along the course of the River Swale and often form flat lying land used by farmers in the past for haymaking. River terraces can be encountered along many of the Upper Swaledale becks and River Swale.